The role of chromosomal proteins in maintaining the structure and regulating the function of chromatin and chromosomes is investigated. Present efforts are concentrated on learning the cellular function of two non-histone chromosomal proteins, HMG- 14 and HMG-17. These two proteins are the only known nucleoproteins whose main binding site in the nucleus is on the nucleosome. Various experiments suggest that may be involved in modulating the structure of transcriptionally active chromatin. We have isolated and sequenced the human cDNAs for both HMG- 14 and HMG-17. We found that the transcripts that unusual features including extremely long 3' untranslated regions (65% of the sequence) and highly GC-rich 5' untranslated regions (73% GC). Each of the proteins is encoded by a distinct multigene family. The HMG-17 multigene family is the largest known human retropseudogene family with 50 copies per genome. Each family transcribes a single-size mRNA whose synthesis is regulated in a cell-cycle specific manner. The sequences of the two cDNAs are distinct except in the region coding for the DNA binding domains of the proteins. The DNA binding domains of the proteins are similar in many ways, suggesting that they recognize distinct regions on the nucleosome. Transfection of various HMG- 14 and HMG-17-containing vectors into COS and yeast cells allows modulation of the cellular level of the proteins. These studies will further the understanding of gene structure and function in normal and neoplastic cells.